1. Field of the Invention
The present invention relates to measuring devices and, more particularly, to transducers for sensing fluid pressure in a tubular conduit.
2. The Prior Art
In the past a variety of pressure transducers have been proposed which employ a number of different principles. In one class of devices, represented by, e.g., Ostergren U.S. Pat. Nos. 2,420,148 and Kooiman 3,079,576, strain gages are applied directly to the surface of a fluid-transporting conduit. Changes in pressure within the conduit cause a slight expansion or contraction in the diameter of the pipe, thus causing the strain gage to register a change in resistance.
A second class of devices, represented, e.g., by Alibert et al. U.S. Pat. Nos. 3,603,152 and Vasek 3,698,248, employ piezo-electric elements held in contact with a conduit by a fixture which may be removable. Changes in pressure within the conduit are represented by slight voltage variations produced by the piezo-electric element when it is stressed by the expansion of the conduit.
In a third class of devices, the expansion or contraction of the pipe is multiplied by a mechanical multiplier to increase the pressure applied to the sensing element. This class of devices is represented by, e.g., Weaver U.S. Pat. No. 3,698,249.
All of the above devices suffer from a common drawback: their output signals are weak and require considerable voltage and power amplification before they may be put to useful work. For the second and third categories of devices, the cost of fixtures must be counted as a drawback since much expensive machine work is required to produce them.
Since many applications for pressure transducers contemplate that eventually the output of the transducer will be used to produce useful work, it is required for those applications that a sufficiently high power output be available. When amplification is required to fulfill this requirement, the cost of using the succeeding amplifer stages must be added to the cost of the transducer.
The present invention is intended to remedy these drawbacks by providing a new and useful pressure transducer having a current output large enough in magnitude to directly operate lamps, control valves, solenoid relays and the like without need for intervening electronic amplification.